1. Field of the Invention
The present invention relates to a liquid ejection apparatus for ejecting liquid such as ink, and a printing apparatus provided with the liquid ejection apparatus.
2. Description of the Related Art
As a liquid ejection apparatus that jets liquid onto a target, an ink ejection apparatus applied to an inkjet printing apparatus is known. The ink ejection apparatus of the inkjet printing apparatus is typically provided with an ink cartridge, and a printing head that is supplied with ink in the ink cartridge. The printing head has an ejection port (nozzle) for ejecting (jetting) the ink; is mounted on a carriage that moves with respect to a printing material; and is moved with respect to the printing material. The ink ejection apparatus can eject the ink from the ejection port at a desired position and desired timing with respect to the printing material so as to form an image including pictures, lines, characters, and the like on the printing material.
For the ink cartridge, a configuration in which the ink cartridge can be detachably attached onto the carriage mounted with the printing head may be employed. On the other hand, a configuration in which the ink cartridge is arranged with being separated from the carriage (referred to as an off carriage type) is also known. Such an off carriage type ink cartridge is configured to supply ink to a printing head mounted on the carriage through a flexible tube. An inkjet printing apparatus provided with such an off carriage type ink cartridge can mount a large volume ink cartridge thereon, and therefore has an advantage that even in the case of large volume printing, a replacement frequency of the ink cartridge is low.
In the case of the inkjet printing apparatus provided with such an off carriage type ink cartridge, when a large-sized printing material is handled, a length for routing the tube for ink supply is increased. This may result in an increase in dynamic pressure (pressure loss) of the ink from the ink cartridge to the carriage, and the occurrence of a pressure variation in the ink due to acceleration/deceleration of the carriage. Accordingly, in such a case, it is difficult for such an inkjet printing apparatus to stably eject the ink from the printing head.
For this reason, the inkjet printing apparatus provided with such an off carriage type ink cartridge employs a configuration in which a sub-tank that can retain the ink is mounted on the carriage, and the ink inside the ink cartridge is transported under pressure to the sub-tank. Note that the ink supplied to the sub-tank is, after its pressure has been adjusted in the sub-tank, supplied to the printing head. An example of an inkjet printing apparatus having such a configuration is disclosed in Japanese Patent No. 3606282.
An ink supply apparatus of an inkjet printing apparatus in Japanese Patent No. 3606282 is, in a sub-tank, provided with a valve unit that has a self sealing function. The valve unit is provided with: an ink supply chamber that is connected to an ink cartridge through a tube; a valve that opens/closes a supply path; a biasing member that biases the valve so as to close the supply path; and a pressure chamber and a film member for opening the valve. Note that the pressure chamber is brought to negative pressure due to ink ejection from a printing head, and due to the negative pressure, the film member operates so as to open the valve. Also, such a sub-tank in Japanese Patent No. 3606282 is provided with a filter chamber on an ink cartridge side with respect to the valve, in the supply path. The filter chamber has a foreign matter removing function, and also has a function to prevent a bubble in ink from reaching the printing head. A bubble captured by a filter member of the filter chamber can accumulate in a vertically upper part within the filter chamber. Note that a volume of a space where such a bubble accumulates is finite, and therefore in the inkjet printing apparatus, such a bubble can be periodically discharged by discharge operation that applies negative pressure from an ejection port, but cannot be completely removed.
The above-described filter chamber plays a role of removing the bubble from the ink as described above; however, on the other hand, in order to prevent the ink from ending, it is required to ensure that the ink passes through the filter member. However, in the filter chamber of the sub-tank in Japanese Patent No. 3606282, due to a flow path configuration of the supply path, a space region for bubble accumulation may be expanded to a periphery of an ink supply port to the filter chamber. For this reason, when the ink is supplied, a bubble in the filter chamber may be pressed by ink flow; brought into contact with the filter member; and cover part or all of a surface of the filter member. This causes an effective area of the filter member to be reduced, which may affect ink supply.
In order to prevent a bubble from being brought into contact with the filter member in the filter chamber having a finite volume, for example, it is necessary to frequently perform the above-described bubble discharge operation to keep a predetermined amount of ink or more between the bubble accumulating in the filter chamber and the filter member. However, such a countermeasure means an increase in the number of performances of the discharge operation, and therefore may result in an increase in amount of ink that is uselessly discharged with a bubble.